Inner substrate for manufacturing multilayer printed circuit boards

ABSTRACT

An exemplary inner substrate for manufacturing multilayer printed circuit boards is provided. The inner substrate has a number of substrate units and a number of transverse folding portions alternately arranged along a longitudinal direction of the inner substrate. Each of the substrate units is configured for forming a unitary printed circuit board. Each of the folding portions is interconnected between neighboring substrate units. Each of the folding portions defines at least one line of weakness perpendicular to the longitudinal direction of the inner substrate for facilitating folding and unfolding the neighboring substrate units to each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the benefitof U.S. patent application Ser. No. 11/959,212 filed Dec. 18, 2007,entitled “METHOD FOR MANUFACTURING MULTILAYER PRINTED CIRCUIT BOARDSUSING INNER SUBSTRATE”, the entire contents of which are incorporatedherein by reference.

BACKGROUND

1. Technical Field

The present invention relates to printed circuit boards, and moreparticularly relates to an inner substrate for manufacturing multilayerprinted circuit boards and a method for manufacturing multilayer printedcircuit boards using the inner substrate.

2. Description of Related Art

In order to accommodate development of miniaturization and multifunctionof electronic products, multilayer printed circuit boards are widelyused due to their characteristics such as micromation, light quality,high-density interconnection.

Multilayer printed circuit boards usually include multilayer rigidprinted circuit boards and multilayer flexible printed circuit boards.Nowadays, multilayer printed circuit boards are manufactured using atypical sheet-by-sheet process. However, only one multilayer printedcircuit board can be manufactured at a time, using the typical methoddescribe above. Thus, efficiency of manufacturing multilayer printedcircuit boards is low and cost of manufacturing multilayer printedcircuit boards is high.

Currently, flexible printed boards can be manufactured using aroll-to-roll process that is a substitute of a typical sheet-by-sheetprocess. The roll-to-roll process can enhance efficiency ofmanufacturing flexible printed boards. However, a multilayer flexibleprinted circuit board is generally thicker than a single layer flexibleprinted circuit board, flexibility of the multilayer flexible printedcircuit board is low. Thus, it is difficult for the multilayer flexibleprinted circuit board to be wrapped around a roller. Therefore, theroll-to-roll process for manufacturing the single flexible printedcircuit board is not suitable for manufacturing the multilayer flexibleprinted circuit board. Therefore, multilayer flexible printed circuitboards are still manufactured using the sheet-by-sheet process liketypical multilayer rigid printed circuit boards. Thus, efficiency ofmanufacturing multilayer flexible printed circuit boards is also low andcost of manufacturing multilayer flexible printed circuit boards is alsohigh.

What is needed, therefore, is an inner substrate for manufacturingmultilayer printed circuit boards and a method for manufacturingmultilayer printed circuit boards using the inner substrate, therebyimproving efficiency of manufacturing multilayer printed circuit boards.

SUMMARY

One present embodiment provides an inner substrate for manufacturingmultilayer printed circuit boards. The inner substrate has a number ofsubstrate units and a number of transverse folding portions alternatelyarranged along a longitudinal direction of the inner substrate. Each ofthe substrate units is configured for forming a unitary printed circuitboard. Each of the folding portions is interconnected betweenneighboring substrate units. Each of the folding portions defines atleast one line of weakness perpendicular to the longitudinal directionof the inner substrate for facilitating folding and unfolding theneighboring substrate units to each other.

Another present embodiment provides a method for multilayer printedcircuit boards. In the method, firstly, an elongated inner substratehaving a number of substrate units and a number of transverse foldingportions alternately arranged along a longitudinal direction of theinner substrate is formed. Each of the substrate units is configured forforming a unitary printed circuit board. Each of the folding portions isinterconnected between neighboring substrate units. Each of the foldingportions defines at least one line of weakness perpendicular to thelongitudinal direction of the inner substrate. Secondly, at least onecircuit substrate is laminated on each of the substrate units. Thirdly,the inner substrate is folded in a manner such that at least two of thesubstrate units are stacked one on another. Fourthly, the stackedsubstrate units are unfolded. Fifthly, the at least one circuitsubstrate on each of the unfolded substrate units is processed.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present embodiments can be better understood withreference to the following drawings. The components in the drawings arenot necessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the present embodiments.Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is a schematic view of an inner substrate according to a presentembodiment.

FIG. 2 is a schematic, cross-sectional view of the inner substrate inFIG. 1.

FIG. 3 is a schematic view of another inner substrate according to thepresent embodiment.

FIG. 4 is a schematic, cross-sectional view of the inner substrate inFIG. 3.

FIG. 5 is a schematic view of further another inner substrate accordingto the present embodiment.

FIG. 6 is a schematic, cross-sectional view of the inner substrate inFIG. 5.

FIG. 7 is a schematic, cross-sectional view of an inner substrate havingcircuit substrates laminated thereon according to the presentembodiment.

FIG. 8 is a schematic, cross-sectional view of folding of the substrateunits of an inner substrate having circuit substrates laminated thereonaccording to the present embodiment.

FIG. 9 is a schematic, cross-sectional view of unfolding and folding ofthe substrate units of an inner substrate having circuit substrateslaminated thereon according to the present embodiment.

FIG. 10 is a schematic view of an inner substrate having conductiveadhesive tapes attaching thereon.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments will now be described in detail below and with reference tothe drawings.

Referring to FIG. 1 and FIG. 2, an exemplary inner substrate 10 formanufacturing multilayer printed circuit boards is shown. The innersubstrate 10 is elongated tape-shaped. The inner substrate 10 can be arigid printed circuit substrate or a flexible printed circuit substrate.The inner substrate 10 can be a single-layer structure or a multilayerstructure containing two layers, four layers, six layers or more. In thepresent embodiment, referring to FIG. 2, the inner substrate 10 is adouble-sided structure. The inner substrate 10 includes an insulatingbase film and two electrically conductive layers formed on two oppositesides of the insulating base film. The inner substrate 10 has a numberof substrate units 11 and a number of transverse folding portions 20alternately arranged along a longitudinal direction thereof.

In detail, the substrate units 11 are arranged along a longitudinaldirection of the inner substrate 10. Each of the substrate units 11includes an insulating layer 12 (i.e., the insulating base film of theinner substrate 10) and two conductive circuit layers 13 (i.e., thecorresponding electrically conductive layer of the inner substrate 10).The conductive circuit layers 13 are configured for forming conductivecircuit patterns on two opposite sides of the insulating layer 12,respectively. Each of the substrate units 11 can be configured forforming a unitary printed circuit board. Each of the folding portions 20interconnects the two neighboring substrate units 11. Thus, the foldingportions 20 are also arranged along a longitudinal direction of theinner substrate 10. Therefore, it is noted that the inner substrate 10is divided into a number of the substrate units 11 by the foldingportions 20.

Each of the folding portions 20 defines two line of weaknesses includinga first line 211 and a second line 212 both perpendicular to thelongitudinal direction of the inner substrate 10, for facilitatingfolding and unfolding the neighboring substrate units 11 with/from eachother. The first line 211 is parallel to the second line 212. Each ofthe folding portions 20 defines a number of first through-holes 21aligned in the first line 211 and a number of second through-holes 22aligned in the second line 212. A distance between the first line 211and the second line 212 is determined by a thickness of thecorresponding multilayer printed circuit board finally produced.Generally, the distance between the first line 211 and the second line212 is either equal to or larger than a total thickness of twoneighboring stacked substrate units 11 of the inner substrate 10 and twocircuit substrates sandwiched between the stacked substrate units 11once the inner substrate 10 has been folded. That is, at least onecircuit substrate is laminated onto each of the two neighboringsubstrate units 11, on an identical side of the inner substrate 10, andthen later on the two adjacent circuit substrates on the identical sideof the inner substrate 10 become sandwiched between the two neighboringsubstrate units 11 during folding of the inner substrate 10. For moredetails, please refer to the description provided below in relation toFIG. 7.

Additionally, in general, the thicknesses of the two circuit substratessandwiched between any two neighboring stacked substrate units 11 may bethe same or may be different. Accordingly, the distance between thefirst line 211 and the second line 212 of each folding portion 20 can beidentical with that of the other folding portions 20 or different fromthat of any or all of the other folding portions 20. Because theweakness of the inner substrate 10 at the first through-holes 21 and thesecond through-holes 22, the flexibility of inner substrate 10 isincreased, especially/particularly at the area of the firstthrough-holes 21 and the second through-holes 22. Thus, the innersubstrate 10 can be folded or unfolded at the first through-holes 21along the first line 211 and the second through-holes 22 along thesecond line 212.

It is noted that the folding portions 20 can be in other structures.

Referring to FIGS. 3 and 4, another exemplary inner substrate 30 formanufacturing multilayer printed circuit boards is shown. The innersubstrate 30 is similar to the inner substrate 10 except for foldingportions 35. Each of the folding portions 35 defines a line of weaknessincluding a third line 350 for facilitating folding and unfolding theneighboring substrate units 31 with/from each other. The third line 350extends perpendicularly to a longitudinal direction of the innersubstrate 30. Each of the folding portions 35 defines a groove 351 onone side thereof along the third line 350. A width of the groove 351 isdetermined by a thickness of the corresponding multilayer printedcircuit board finally produced. Generally, the width of the groove 351is either equal to or larger than a total thickness of e two neighboringstacked substrate units 31 of the inner substrate 30 and two circuitsubstrates sandwiched between the stacked substrate units 31 once theinner substrate 30 has been folded. That is, at least one circuitsubstrate is laminated onto each of the two neighboring substrate units31, on an identical side of the inner substrate 30, and then later onthe two adjacent circuit substrates on the identical side of the innersubstrate 30 become sandwiched between the neighboring substrate units31 during folding of the inner substrate 30. It is noted that each ofthe folding portions 35 can define a groove 351 at each of the twoopposite sides of the inner substrate 30.

Referring to FIGS. 5 and 6, further another exemplary inner substrate 40for manufacturing multilayer printed circuit boards is shown. The innersubstrate 40 is similar to the inner substrate 10 except the foldingportions 45. Each of the folding portions 45 defines a first groove 451along a first line 450 and a second groove 453 along a second line 452.It is noted that each of the folding portions 45 can define a firstgroove 451 along the first line 450 respectively on two opposite sidesof the inner substrate 40 and a second groove 453 along the second line452 respectively on two opposite sides of the inner substrate 40.

Multilayer printed circuit boards can be manufactured using the innersubstrate 10, 30, or 40, as described above. In the present embodiment,the method for manufacturing multilayer printed circuit boards using theinner substrate 10 includes the following steps.

Step 1: the inner substrate 10, as described above, is formed.

In the present embodiment, the inner substrate 10 is a single-layerdouble-sided structure, therefore, the inner substrate 10 can be formedwith a double-sided copper-clad substrate. A large sheet of rawdouble-sided copper-clad substrate is divided into a number of elongatedtape-shaped double-sided copper-clad substrate according to sizes ofmultilayer printed circuit boards. The elongated tape-shapeddouble-sided copper-clad substrate can be wrapped around a roller and beconfigured for forming the inner substrate 10. The conductive circuitlayer 13 on the two opposite sides of the inner substrate 10 can beformed with two copper foils of the double-sided copper-clad substrateusing a photolithographic process or a laser ablation process.

The folding portions 20 can be formed before or after the conductivecircuit layers 13 are formed. The folding portions 20 can be formedusing a laser drilling process, a mechanical drilling process or achemical etching process.

Step 2: at least one circuit substrate is laminated on each of thesubstrate units 11 of the inner substrate 10.

For the purpose of illustration only, in the present embodiment, each ofthe substrate units 11 of the inner substrate 10 has two circuitsubstrates laminated on two opposite sides thereof, respectively. It isnoted that in alternative embodiments, each of the substrate units 11 ofthe inner substrate 10 can have only one circuit substrate laminated ononly one side thereof. The circuit substrates laminated can be rigidprinted circuit substrates or flexible printed circuit substrates. Thecircuit substrates can be single-layer structures, or multilayerstructures containing two layers, four layers, six layers or more. Inthe present embodiment, each of the circuit substrates is a single-sidedstructure that including an insulating layer and an electricallyconductive layer. During laminating the circuit substrates, theinsulating layer of each of the circuit substrates is in contact withthe corresponding conductive circuit layer 13 of the correspondingsubstrate unit 11. Thereby, the circuit substrates are laminated ontothe two opposite sides of the substrate unit 11.

In detail, referring to FIG. 7, the inner substrate 10 can be providedusing a roller 15. The inner substrate 10 includes a first substrateunit 111, a second substrate unit 112, a third substrate unit 113, afirst folding portion 201 and a second folding portion 202. The firstfolding portion 201 interconnects the first substrate unit 111 and thesecond substrate unit 112. The second folding portion 202 interconnectsthe second substrate unit 112 and the third substrate unit 113. Duringlaminating, a first circuit substrate 301 and a second circuit substrate401 are laminated onto two opposite sides of the first substrate unit111, respectively. A third circuit substrate 302 and a fourth circuitsubstrate 402 are laminated onto two opposite sides of the secondsubstrate unit 112, respectively. A fifth circuit substrate 303 and asixth circuit substrate 403 are laminated onto two opposite sides of thethird substrate unit 113, respectively.

In the present embodiment, the first circuit substrate 301, the secondcircuit substrate 401, the third circuit substrate 302, the fourthcircuit substrate 402, the fifth circuit substrate 303 and the sixthcircuit substrate 403 have an identical thickness. It is noted that thefirst circuit substrate 301, the second circuit substrate 401, the thirdcircuit substrate 302, the fourth circuit substrate 402, the fifthcircuit substrate 303 and the sixth circuit substrate 403 can havedifferent thicknesses. Each of the first circuit substrate 301, thesecond circuit substrate 401, the third circuit substrate 302, thefourth circuit substrate 402, the fifth circuit substrate 303 and thesixth circuit substrate 403 has at least one electrically conductivelayer. It is noted that a circuit pattern can be preformed in the atleast one electrically conductive layer. Alternatively, the circuitpattern could be formed in a later step, e.g. after the step ofunfolding the inner substrate, which should also be considered to havethe same meanings of “circuit substrates” of the present invention.

Step 3: the inner substrate 10 is folded in a manner such that at leasttwo of the substrate units 11 are stacked one on another.

In detail, in order to stack the second substrate unit 112 on the firstsubstrate unit 111, a distance between the first line of the firstthrough-holes 2011 and the second line of the second through-holes 2012of the first folding portion 201 is equal to a total thickness of theinner substrate 10, the first circuit substrate 301 laminated onto thefirst substrate unit 111 and the third circuit substrate 302 laminatedonto the second substrate unit 112. Referring FIG. 8, after laminating,the inner substrate 10 can be folded at the first folding portion 201,and thus the second substrate unit 112 is stacked on the first substrateunit 111. In such configuration, the third circuit substrate 302laminated onto the second substrate unit 112 can contact with anddisposed onto the first circuit substrate 301 laminated onto the firstsubstrate unit 111. Thus, the first circuit substrate 301 and the thirdcircuit substrate 302 are sandwiched between the first substrate unit111 and the second substrate unit 112.

Similarly, in order to stack the third substrate unit 113 on the secondsubstrate unit 112, a distance between the first line of the firstthrough-holes 2021 and the second line of the second through-holes 2022of the second folding portion 202 is equal to a total thickness of theinner substrate 10, the fourth circuit substrate 401 laminated onto thesecond substrate unit 112 and the sixth circuit substrate 403 laminatedonto the third substrate unit 113. The inner substrate 10 can also befolded at the second folding portion 202, and thus the third substrateunit 113 is stacked on the second substrate unit 112. In suchconfiguration, the sixth circuit substrate 403 laminated onto the thirdsubstrate unit 113 can be in contact with and disposed onto the fourthcircuit substrate 402 laminated onto the second substrate unit 112. Thefourth circuit substrate 401 and the sixth circuit substrate 403 aresandwiched between the second substrate unit 112 and the third substrateunit 113. Similarly, multiple substrate units 11 laminated with circuitsubstrates can be stacked one by one in the manner described above.

Additionally, because the circuit substrates are laminated onto thesubstrate units 11 using an adhesive, the surplus adhesive may overflowfrom the edges of the substrate units 11 and the circuit substratesduring laminating. When the substrate units 11 are stacked one by one,the surplus adhesive may overflow and cause the substrate units 11 toadhere to each other. Thus, it is difficult for the substrate units 11to be stacked or unstacked repeatedly. Advantageously, when onesubstrate unit 11 is stacked on another substrate unit 11, a separatingfilm (not shown) can be interposed between the two neighboring stackedsubstrate units 11. For example, in the present embodiment, oneseparating film can be interposed between the third circuit substrate302 laminated onto the second substrate unit 112 and the first circuitsubstrate 301 laminated onto the first substrate unit 111, and anotherseparating film can be interposed between the sixth circuit substrate403 laminated onto the third substrate unit 113 and the fourth circuitsubstrate 402 laminated onto the second substrate unit 112.

Step 4: the stacked substrate units 11 are unfolded.

Generally, a process for manufacturing multilayer printed circuit boardsusing the substrate units of the inner substrate 10 includes the step ofdrilling holes in the circuit substrates, forming electrical traces onthe circuit substrates, electroplating gold on terminals of theelectrical traces, laminating protective films on the circuitsubstrates, inspecting electrical connection and external appearance,and so on. Therefore, the stacked substrate units may need to beunfolded to undergo these steps.

It is understood that the inner substrate 10 stacked as described abovecan be unfolded at the first folding portion 201 and the second foldingportion 202. Thus the third substrate unit 113 can be unstacked from thesecond substrate unit 112, and the second substrate unit 112 canunstacked from the first substrate unit 111. Similarly, multiplesubstrate units 11 can be unstacked one by one. When one substrate unit11 is unstacked from the other substrate units 11, sequential steps toform multilayer printed circuit boards, for example, forming outsideelectrical traces on the circuit substrates, electroplating gold onterminals of the electrical traces, and laminating protective films onthe circuit substrates, can be performed.

Step 5: the at least one circuit substrate on each of the unfoldedsubstrate units 11 is processed.

The sequential steps includes drilling holes in the circuit substrates,forming outside electrical traces on the circuit substrates,electroplating gold on terminals of the electrical traces, laminatingprotective films on the circuit substrates, inspecting electricalconnection and external appearance, and so on. In these steps, referringto FIG. 9, multilayer printed circuit boards can be manufactured usingthe substrate units 11 of the inner substrate 10 in a manner such thatthe inner substrate 10 is unfolded at the folding portions 20. When onesubstrate unit 11 is unfolded from a stack of the substrate units 11,one of the steps of drilling holes in the circuit substrates, formingoutside electrical traces on the circuit substrates, electroplatinggold, laminating protective films on the circuit substrates, andinspecting electrical connection and external appearance, can beperformed on the one unfolded substrate unit 11.

It is understood that, after one substrate unit 11 has undergone one ofthe steps of drilling holes in the circuit substrates, formingelectrical traces on the circuit substrates, electroplating gold onterminals of the electrical traces, laminating protective films on thecircuit substrates, and inspecting electrical connection and externalappearance, the one unfolded substrate unit 11 can be stacked on theother substrate units 11 again. For example, as shown in FIG. 9, the oneunfolded substrate unit 11 can be stacked on the other substrate units11 that have already undergone the same step. It is also understood thatsome steps can be performed on the stacked substrate units 11. Forexample, a baking step can be performed after the substrate units 11laminated with the circuit substrates are stacked together.

Preferably, in the step of electroplating gold on terminals of theelectrical traces, at least a conductive adhesive tape 50 can beattached on the inner substrate 10, as shown in FIG. 10. The conductiveadhesive tape 50 is configured for connecting the two neighboringsubstrate units 11 so as to electrically connect the conductive circuitpatterns formed with conductive circuit layers 13 of the two neighboringsubstrate units 11. The conductive adhesive tape 50 can be attached ontothe conductive circuit layers 13 using a method such as a thermalattachment or an ultrasonic attachment.

While certain embodiments have been described and exemplified above,various other embodiments will be apparent to those skilled in the artfrom the foregoing disclosure. The present invention is not limited tothe particular embodiments described and exemplified but is capable ofconsiderable variation and modification without departure from the scopeof the appended claims.

1. An inner substrate for manufacturing multilayer printed circuitboards, the inner substrate comprising: a plurality of substrate unitsand a plurality of transverse folding portions alternately arrangedalong a longitudinal direction of the inner substrate, each of thesubstrate units being configured for forming a unitary multilayerprinted circuit board, each of the folding portions being interconnectedbetween two neighboring substrate units, each of the folding portionsdefining at least one line of weakness perpendicular to the longitudinaldirection of the inner substrate for facilitating folding and unfoldingthe inner substrate.
 2. The inner substrate of claim 1, wherein the atleast one line of weakness includes a first line and a second lineparallel to the first line, each of the folding portions comprising aplurality of first through-holes aligned in the first line and aplurality of second through-holes aligned in the second line.
 3. Theinner substrate of claim 2, wherein the inner substrate includes aninsulating base film and two electrically conductive layers formed ontwo opposite sides of the insulating base film, and the firstthrough-holes and the second through-holes penetrate through theinsulating base film and the electrically conductive layers.
 4. Theinner substrate of claim 2, wherein the distance between the first lineand the second line of each folding portion is equal.
 5. The innersubstrate of claim 2, wherein the distance between the first line andthe second line of one folding portion is different from that of anotherfolding portion.
 6. The inner substrate of claim 1, wherein each of thefolding portions defines at least one groove in at least one sidethereof along the at least one line of weakness.
 7. The inner substrateof claim 6, wherein the inner substrate includes an insulating base filmand two electrically conductive layers formed on two opposite sides ofthe insulating base film, and a thickness of the at least one groove islarger than a thickness of one of the electrically conductive layers andless than a sum of thicknesses of the insulating base film and one ofthe electrically conductive layers.
 8. The inner substrate of claim 1,wherein each of the folding portions defines at least one groove in ateach of the two opposite sides of the inner substrate along the at leastone line of weakness.
 9. The inner substrate of claim 1, wherein the atleast one line of weakness includes a first line and a second line, eachof the folding portions comprising a first groove in at least one sidethereof along the first line and a second groove in at least one sidethereof along the second line parallel to the first line.
 10. The innersubstrate of claim 8, wherein the distance between the first line andthe second line of each folding portion is equal.
 11. The innersubstrate of claim 8, wherein the distance between the first line andthe second line of one folding portion is different from that of anotherfolding portion.
 12. The inner substrate of claim 1, wherein the atleast one line of weakness includes a first line and a second lineparallel to the first line, each of the folding portions comprising afirst groove respectively at two opposite sides of the inner substratealong the first line and a second groove respectively at two oppositesides of the inner substrate along the second line.
 13. The innersubstrate of claim 1, wherein each of the substrate units includes atleast one insulating layer and at least one electrically conductivelayer formed on the dielectric layer.